I need help, badly

While this is not about me, it is about my parents. My father was an alcoholic, during this time he had extreme mood swings and would verbally lash out at any moments notice. It got to the point where my mom felt embarrassed to be in public with him because he would yell at her. He is now sober and nothing has changed, except for him developing this idea that my mother is cheating. He has tried to "catch her" for two years now, and has found nothing. He follows her home from work, stalks her coworkers profiles, and even asks why she is driving next to a certain type of car, because in his mind whoever he thinks she is cheating on him with drives this type of car.

It has gotten very bad, and my mother knows she needs to leave. However she can't leave because he has told her that he will ruin her life. He said he will call where she works, and say that she touches her very young students. Which SHE WOULD NEVER DO. But once you get an accusation like that one in education, your career is done.

I just feel so terrible about the whole situation, and that I can't help it. I have to just listen to it and I don't know what to do anymore. I'm posting today because my mom asked me for help and I feel so terrible for not being able to help her.

Any advice or supportive words is welcome, but I would love advice if there is any to give.

Thank you.